Prevention of icing of electrical conductors



A ril 25, 1967 E. TOMS ETAL 3,3

PREVENTION OF ICING OF ELECTRICAL CONDUCTORS Filed April 26, 1965 United States Patent Ofifice 3,3 16,345 Patented Apr. 25, 1967 3,316,345 PREVENTION OF ICING OF ELECTRICAL CONDUCTORS James Edward Toms, Leeds, and David Alan Kidd, Bil- This invent-ion relates to the prevention of ice formation or the melting of ice on electrical conductors carrying alternating current and is applicable for example to overhead electrical conductors in transmission lines and to other exposed electrical conductors which may be subject to possible ice formation, for example moving or fixed contacts in outdoor substation switching equipment.

In the specification of the copending application Serial No. 405,587 there is described an electrical conductor in which ice formation is prevented or ice is melted by surrounding the conductor with a magnetic material having a Curie temperature within the range C. to 20 C. At temperatures above the Curie temperature the material would be non-magnetic and therefore power losses due to eddy currents and/ or magnetic hysteresis arising from the passage of an alternating current through the conductor would be very small when the temperature is above the Curie temperature. When the ambient temperature drops below the Curie temperature of the magnetic material and the temperature of the surface of the conductor assembly falls, the material surrounding the conductor becomes magnetic and hence eddy current and/ or magnetic hysteresis losses will increase and so will raise the surface temperature. An equilibrium surface temperature will be reached and, provided this is above 0 C., no ice can form on the conductor assembly.

According to the present invention, an electrical conductor has the magnetic material with a Curie temperature within the range 0 C. to 20 C. formed as a tape which is put on the conductor. The tape for example may be wound helically around the conductor. This construction facilitates the application of the material where required; for example it may be put on the conductor for a short length in the middle of each span between supporting towers. It will be appreciated that since the conductor hangs as a catenary, water will run down the conductor to the lowest point which is the middle of the span if the end points are at the same level and thus ice formation tends to be most serious at the middle of the span. It is generally desirable to minimise additional weight on the conductors and the use of a tape enables the material to be put on only where necessary.

If the magnetic material is applied as a helically wound tape, the winding is preferably open, that is to say the pitch of the turns is greater than (for example twice) the width of the tape.

Preferably the tape is applied in short lengths so that, in the event of a tape being unwound from the conductor, it would not be long enough to reach to and make contact with an adjacent conductor. It is readily possible however to secure the tape firmly at each end for example by crimping or binding with wire.

A further advantage arising from putting the magnetic material around the conductor is that the permeability of the material is very much greater than unit-y at the Curie temperature but falls off at higher temperatures. At the Curie temperature, the high permeability and leakage fluxes cutting the conductor cause the whole conductor assembly to act as if its permeability was greater than unity with the result that the current flows in the outer part of the assembly due to the well known skin effect and the effective resistance to alternating current ductor 10 on which a tape is substantially greater than the direct current resistance thereby further improving the heating effect. I

The magnetic tape material may be a metallic alloy and in this case most of the heating will be due to eddy current losses in the covering. A suitable alloy having a Curie temperature just above 0 C. is a quaternary alloy of nickel, iron, chromium and silicon; one suit-able material is an alloy containing 9.14% chromium, 34-38% nickel, 0.51.15% silicon and the balance iron.

Alternatively the material may be a ferrite material. Such ferrite material may be dispersed in a suitable plastic matrix. The Curie temperature of a ferrite can readily be adjusted to the required value. With a ferrite, nearly all the heating effect is due to the magnetic hysteresis loss in the material. Manganese zinc and nickel zinc ferrites have very suitable magnetic properties.

As previously stated, for the present invention, material having a Curie temperature between 0 C. and 20 C. is employed. Preferably the Curie temperature is between 0 C. and 10 C.

The heating produced by hysteresis and/or eddy current loss is increased by placing a shorted turn round the ferrite or magnetic alloy forming the tape so that the device would then operate as a single turn current transformer whose transformation ratio would be temperature sensitive.

It will be seen that the material may readily be applied to exposed conductors in most situations where icing may occur. The heating of the conductors is effected automatically when the surface temperature drops below the Curie point of the material and no external supply circuits or control circuits are required. Power is dissipated only when the temperature has dropped below the Curie point and thus only when it is necessary to start heating the conductor to prevent ice formations.

The invention furthermore includes within its scope, an element for preventing ice formation on an electrical conductor comprising a tape of magnetic material having a Curie temperature within the range 0 C. to 20 C. and electrically conductive material around the magnetic material so as to form a shorted secondary turn when the tape is put on a conductor carrying alternating current.

In the following description, reference will be made to the accompanying drawings in which:

FIGURE 1 is a view in elevation of a conductor with a helical tape of magnetic material illustrating one embodiment of the invention; and

FIGURES 2 and 3 are sect-ions through two different forms of tape used in the arrangement of FIGURE 1.

Referring to FIGURE 1, there is illustrated a con- 11 is wound to form an open helix. Typically for a conductor of an overhead power transmission line the tape 11 may be 0.79 inch wide by 0.079 inch thick and wound on the conductor in an open helix with a pitch such that the spacing between adjacent turns is between and 1% inches. Conveniently each length of tape extends about a yard along the conductor and is secured at each end by a clamp. The tape is formed of a magnetic material having a Curie temperature between 0 C. and 20 C. and preferably bet-ween 0 C. and 10 C. For such a tape, a suitable metal alloy is conveniently used, e.g. a quaternary alloy of nickel, iron, chromium and silicon having by percentage weight, 9l4% chromium, 3438% nickel, 0.5- 1.15% silicon and the remainder iron. A typical example has the composition nickel 35.23%, chromium 10.8%, silicon 1.05% and the residue iron. Alternatively, ferrite particles may be dispersed in a plastic matrix formed into a tape; typically the ferrite material might constitute between 20% and by volume of the tape,

this material being dispersed in a plastic matrix formed, for example, of polyvinyl chloride or polyethylene.

The accompanying drawings illustrate the conductors diagrammatically. Conductors for hearing currents are usually formed of stranded aluminum or copper which is helically arranged around a steel core. The current tends to follow the helical path of the conducting strands and the magnetic flux at any point on the surface is substantially at right angles to the helical path of the conducting strands at that point. If a helically wound tape is employed, the tape is preferably wound onto the conductor with a. helix of opposite sense to the conducting strands to make a relatively large angle, preferably a right angle, to the conducting strands so as thereby to utilise as far as possible the total magnetic field.

The heating produced by hysteresis and/or eddy current loss in any of the above constructions can be increased by putting a shorted turn around the magnetic material. This may be achieved by coating the tape 11 with a material, e.g. aluminum, having a greater conductivity than said magnetic material. The shorted turn need only be quite thin and, in a typical case might be between 0.005 and 0.040 inch thick depending upon the conductor current and magnetic flux density. Such a coating is shown at .12 in FIGURE 2 which is a crosssectional view of the tape 11 of FIGURE 1. The aluminum shorting turn 12 may be placed around the length of the magnetic tape in the form of a closed loop of tape or may be an electro-deposited layer 12. FIGURE 3 illustrates a conductive shorting turn 13 around a tape 14 formed of ferrite material dispersed in a plastic matrix.

An anti-corrosive insulating layer of, for example, silicon elastomer is preferably put over the aluminum and magnetic materials. The anti-corrosive layer could be a tape wrapping but is preferably a layer applied by painting or spraying. This layer will reduce the ice bond strength and prevent electrolytic corrosion and also insulates the secondary turn from the primary conductor.

It is found that, using the construction described above, at 20 C., the extra heating produced by the low Curie temperature magnetic material is quite small. At 2 C. however, there is very substantial extra heating, even at relatively low power levels. The system however is selfregulating in that, if the temperature of the magnetic material rises, the power dissipated in heat will fall off an-d, if the temperature of this material reaches 20 C., the power loss is very little more than that due to the resistive loss in the conductor.

We claim:

1. An electrical conductor comprising an elongated conductive member and a. tape of magnetic material having a Curie temperature between C. and 20 C. Wound helically around said conductive member, conductive material being arranged around the magnetic material of said tape to form a shorted secondary turn.

2. An electrical conductor as claimed in claim 1 wherein the tape is wound helically around the conductor.

3. An electrical conductor as claimed in claim 2 wherein the tape is wound on an open helix, that is to say, the pitch of the turns is greater than the width of the tape.

4. An electrical conductor as claimed is claim 1 wherein said conductor member is formed of helically laid strands and wherein the tape is wound around the conductive member in a helix of opposite sense to the lay of the strands.

5. An electrical conductor comprising an elongated conductive member and a. tape of magnetic material having a Curie temperature between 0 C. and 20 C. wound helically around said conductive member, said tape having a coating of material of higher electrical conductivity than the magnetic material of the tape.

6. An electrical conductor as claimed in claim wherein said tape is formed of magnetic material coated around its Whole surface with a layer of conductive material.

7. An electrical conductor as claimed in claim 5 wherein the magnetic material is a quaternary alloy of nickel, iron, chromium, and silicon.

8. An electrical conductor as claimed in claim 5 wherein the magnetic material of the tape comprises, by percentage weight, 914% chromium, 34-38% nickel, 0.5-1.15% silicon and the remainder iron.

9. An electrical conductor as claimed in claim 8 wherein the tape has a coating of aluminum.

10. An electrical conductor as claimed in claim 5 wherein the tape is formed of ferrite material dispersed in a plastic matrix.

11. An electrical conductor as claimed in claim 10 wherein the tape has a coating of aluminum.

12. A tape for applying to an electrical conductor comprising particles of ferrite material having a Curie temperature between 0 C. and 20 C. dispersed in a plastic matrix formed as a tape, said plastic matrix having a coating of electrically conductive material.

13. An element for preventing ice formation on an electrical conductor comprising a tape of magnetic material having a Curie temperature Within the range 0 C. to 20 C. and electrically conductive material around the magnetic material so as to form a shorted secondary turn when the tape is put on a conductor carrying alternating current.

14. An element as claimed in claim 13 wherein the magnetic material comprises, by percentage weight, 9- 14% chromium, 34-38% nickel, 0.5-1.l5% silicon and the remainder iron.

15. An element as claimed in claim 13 wherein the magnetic material has a coating of material of higher electrical conductivity than said magnetic material.

16. An electrical conductor comprising an elongated conductive member and a tape of magnetic material having a Curie temperature between 0 C. and 20 C. wound helically around said conductive member, said tape being formed of magnetic material coated around its whole surface with a layer of conductive material.

17. An electrical conductor comprising an elongated conductive member and a tape of magnetic material having a Curie temperature between 0 C. and 20 C. wound helically around said conductive member, the magnetic material of the tape comprising, by percentage weight, 9%14% chromium, 34%-38% nickel, 0.5%1.15% silicon and the remainder iron, the tape having a coating of aluminum.

18. An electrical conductor comprising an elongated conductive member and a tape of magnetic material having a Curie temperature between 0 C. and 20 C. wound helically around said conductive member, the conductive material being arranged around a magnetic material of said tape to form a shorted secondary turn, the magnetic material comprising, by percentage weight, 9%14% chromium, 34%38% nickel, 0.5%1.l5% silicon and the remainder iron.

References Cited by the Examiner UNITED STATES PATENTS 1,586,884 6/1926 Elmen 174-36 X 2,720,604 11/1955 Mitchel et al. -128 X 2,870,311 1/1959 Greenfield et a1. 2,975,339 3/1961 Mitchel et -al 75-128 X 3,009,047 11/1961 Simmons 317-133 X 3,218,384 11/1965 Shaw 174-40 FOREIGN PATENTS 1,282,068 11/ 1961 France.

908,848 10/1962 Great Britain.

LEWIS H. MYERS, Primary Examiner.

H. HUBERFELD, Assistant Examiner. 

13. AN ELEMENT FOR PREVENTING ICE FORMATION ON AN ELECTRICAL CONDUCTOR COMPRISING A TAPE OF MAGNETIC MATERIAL HAVING A CURIE TEMPERATURE WITHIN THE RANGE O* C. TO 20* C. AND ELECTRICALLY CONDUCTIVE MATERIAL AROUND THE MAGNETIC MATERIAL SO AS TO FORM A SHORTED SECONDARY TURN WHEN THE TAPE IS PUT ON A CONDUCTOR CARRYING ALTERNATING CURRENT. 